The present invention relates to means for managing the changeover operation of a solenoid valve, improved by permitting the detection of abnormality before a failure happens and taking precautions in advance by monitoring the changeover operation of the solenoid valve.
In assembling process of, for example, automobiles or other machinery, automatic operation system using compressed air is adopted, and numerous solenoid valves are used for the changeover of compressed air. In such an automatic operation system, operation is continued for a long time in order to increase an efficiency. Therefore, even if only one of the above-mentioned solenoid valve breaks down, the operation of the whole system would be shut down, and this would cause a serious damage. In addition, since the magnitude of the whole system is generally large, it takes a long time to identify the failed solenoid, and to repair or replace it. This would elongate the downtime of the system, and the damage thereby would make the damage more serious.
If a failure of a solenoid valve can be predicted in advance, this problem would be able to be solved. However, effective means therefor have not been proposed.
For example, Japanese Unexamined Utility Model Publication No. 2-66784 discloses a directional control valve wherein a magnet is installed on the outer periphery of a spool, and a magnetic sensor is mounted on a casing, and wherein the changeover of the spool is detected by detecting the magnet by the magnetic sensor.
However, this first known example can only detect whether the spool has been changed over or not. Therefore, if a signal notifying the changeover of the spool is not outputted, it means that the solenoid valve has already been out of working order. That is, this first known example can not predict a failure of a solenoid valve.
Also, Japanese Examined Utility Model Publication No. 7-31021 (Japanese Unexamined Utility Model Publication No. 2-88079) discloses another type of directional control valve wherein a magnet is installed on the piston coupled to an end of a spool, and a detection coil is mounted on a casing, and wherein an induced voltage generated in the detection coil due to the movement of the magnet is detected, whereby an abnormality being detected from the magnitude of this induced voltage. In other words, this is, in principle, of the type which detects the moving speed of the piston, or that of a spool as a induced voltage, and which detects an abnormality from the magnitude of the moving speed.
However, this second known example is of the type which detects the moving speed of the spool during a stroke, and which, if the spool does not move smooth, detects it as a failure. Therefore, for example, if the start of moving of the spool is delayed because of the adhesion of the spool to a stroke end, or if the arrival of the spool is delayed because of the increase in sliding resistance immediately before the arrival at a stroke end, it is impossible for this second known example to detect this abnormality and judge that it is out of working order.
The technical problem of the present invention is to provide operation managing means excellent in detecting accuracy, capable of easily and reliably predicting abnormality of a solenoid valve before failure happens, by detecting operating times of a solenoid valve and discriminating whether the changeover operation is normal or abnormal.
In order to solve the above-describe problems, in accordance with the present invention, there is provided a method for managing the operation of a solenoid valve, wherein operating positions of a valve member for flow passage changeover are detected by a position detecting means attached to the solenoid valve; wherein the operating time from the time point when the driving signal of the solenoid valve is turned on or turned off, to the time point when the valve member moves from a predetermined position or arrives thereat, is measured in a signal processing circuit, from the detected position signal and the clock signal for measurement; wherein whether the changeover operation of the valve member is normal or abnormal is discriminated by comparing these operating time with a plurality of standard values previously inputted in the signal processing circuit; and wherein the display signal in response to the discrimination result is outputted.
In accordance with the above-described method, the operating time from the time point when the solenoid valve is turned on or turned off, to the time point when the valve member moves from a predetermined position or arrives thereat, is measured, and whether the changeover operation of the valve member is normal or abnormal is discriminated from this operating time, and therefore, even if the start of the valve member from a stroke end or the arrival at a stroke end is delayed, it can be reliably detected as an abnormality.
In accordance with a specific embodiment of the present invention, the position at least one stroke end of the valve member is detected by the above-mentioned position detecting means, and at least one time is measured out of the time from the time point when the driving signal of the solenoid valve is turned on or turned off, to the time point when the valve member begins to move from the above-mentioned stroke end, and the time therefrom to time point when it arrives thereat.
In the present invention, the above-mentioned plural standard values comprise a first standard value which indicates the normal range of operating time, and a second standard value which indicates the range where the abnormality of operating time is predicted. When the operating time of the valve member is lower than or equal to the first standard value, a normal signal is outputted; when the operating time of the valve member is between the first standard value and the second standard value, an abnormality predicting signal is outputted; and when the operating time of the valve member is higher than the second standard value, an abnormal signal is outputted.
In accordance with the present invention to implement the above-described method, there is provided a device for managing a solenoid valve, comprising position detecting means which is attached to the solenoid valve and which detects operating positions of a valve member for flow passage changeover; a signal processing circuit for measuring the operating time of the valve member based on position signals from the position detecting means, and discriminating, from the operating time, whether the changeover operation of the valve member is normal or abnormal; wherein the signal processing circuit comprising a measuring section which begins to measure time using an on/off driving signal to a solenoid valve as a start signal, and which measures the operating time up to the changeover of the valve member based on the position signal outputted by said position detecting means; a comparing section which has a plurality of standard values for the preset operating times, and which discriminates whether the changeover operation of the valve member is normal or abnormal, by comparing the operating time of the valve member measured by said measuring section with these plural standard values; and a signal outputting section for outputting a display signal indicating whether the changeover operation of the valve member is normal or abnormal, based on the discrimination result obtained by said comparing section.
In accordance with a specific embodiment of the present invention, the above-described position detecting means is constituted so as to be able to detect the positions at both ends of the valve member; the measuring section of the signal processing circuit comprises a first measuring unit for measuring the time from the time point when the driving signal of the solenoid valve is turned on, to the time point when the valve member begins to move from a first stroke end, a second measuring unit for measuring the time therefrom to the time point when the valve member arrives at a second stroke end, a third measuring unit for measuring the time from the time point when the driving signal of the solenoid valve is turned off, to the time point when the valve member begins to return from the second stroke end, and a forth measuring unit for measuring the return time therefrom to the time point when the valve member arrives at the first stroke end; and the comparing section has first to forth comparators which are connected to above-described measuring units respectively and which compare the operating times measured by these measuring units with the plural standard values.
In the present invention, it is preferable that the above-described position detecting means comprises a magnet disposed so as to move in synchronization with the valve member, and at least one position sensor for detecting magnetic flux from said magnet, and that the position sensor is disposed so as to be able to detect magnetic flux from the magnet over the whole stroke of the valve member.